A memory device having a three-dimensional structure has been proposed in which memory holes are formed in a stacked body in which multiple electrode layers are stacked, and a charge storage film and a semiconductor film are provided to extend in the stacking direction of the stacked body inside the memory hole. The stacked body includes a staircase portion at an end portion of the stacked body. The staircase portion includes multiple terraces. The terraces are portions where the electrode layers are electrically drawn out from the stacked body. Dummy posts for supporting the stacked body in the process of replacing sacrificial layers with the electrode layers are provided in the terraces. It is necessary to ensure a large planar size of the terrace to provide the dummy posts. Therefore, downscaling of the memory device is impeded. It is desirable to reduce the planar size of the staircase portion.